Although autonomic reflex tests have made it possible to diagnose autonomic involvement early in the natural history of diabetes mellitus, there is conflicting evidence as to whether or not asymptomatic patients who perform poorly on autonomic function tests are at increased risk for subsequently developing the typical symptoms of autonomic neuropathy. The purpose of the present study is to explore other methods for identifying patients at risk for developing diabetic polyneuropathy. Our hypothesis is that biochemical predictors evident during the first year of insulin dependent diabetes mellitus will make it possible to identify those patients who subsequently develop deterioration in autonomic function. The following biochemical parameters will be evaluated: 1. Epinephrine and pancreatic polypeptide responses to hypoglycemia 2. Circulating antibodies to the adrenal medulla and autonomic nervous system 3. Plasma prorenin 4.Norepinephrine production This study will focus on the transition from normal autonomic function to subclinical autonomic neuropathy during the first five years of IDDM. The major end points of interest will be performance on cardiovascular autonomic function tests and sudomotor function tests. We will also perform quantitative sensory testing, an alternative measure of small fiber function, and electrodiagnostic studies. The results of these tests will be used to stage the autonomic neuropathy and follow its progression.